Polyamines play a critical role in the control of the innate immune response in the mouse central nervous system.

The present work investigated whether polyamines play a role in the control of the innate immune response in the brain. The first evidence that these molecules may be involved in such a process was based on the robust increase in the expression of the first and rate-limiting enzyme of biosynthesis of polyamines during immune stimuli. Indeed, systemic lipopolysaccharide (LPS) administration increased ornithine decarboxylase (ODC) mRNA and protein within neurons and microglia across the mouse central nervous system (CNS). This treatment was also associated with a robust and transient transcriptional activation of genes encoding pro-inflammatory cytokines and toll-like receptor 2 (TLR2) in microglial cells. The endotoxin increased the cerebral activity of ODC, which was abolished by a suicide inhibitor of ODC. The decrease in putrescine levels largely prevented the ability of LPS to trigger tumor necrosis factor alpha and TLR2 gene transcription in the mouse brain. In contrast, expression of both transcripts was clearly exacerbated in response to intracerebral spermine infusion. Finally, inhibition of polyamine synthesis abolished neurodegeneration and increased the survival rate of mice exposed to a model of severe innate immune reaction in the CNS. Thus, polyamines have a major impact on the neuronal integrity and cerebral homeostasis during immune insults.